Cutting our overall use of fossil fuels has proved a daunting challenge, but it might be possible to get some relief from the effects of climate change by selectively reducing the particulate pollution we produce. Recent research suggests that if we can clean up diesel engines and primitive cookstoves in India and China, for example, that could delay the effects of greenhouse-gas buildup even if pollution from coal-fired power plants persists. A studyreleased last week concludes that if every country were to do what California has done in the last couple of decades to clean up diesel emissions, it would slow down global warming by 15 percent. Reducing similar pollution from sources such as ships and cookstoves—which weren’t included in the study—could help even more.
The study comes as governments in India and China are deciding how to address their increasing pollution, which can contribute to fatal human health problems. Over the weekend, state-controlled media in China announced new pollution rules targeting both power plants and emissions from cars and trucks.
Aerosol pollutants such as sulfur dioxide, soot, and ozone are all bad for human health, but they have different effects on the climate. “Some of the aerosols are warming the planet, and some are cooling the planet,” says Phil Rasch, a fellow at the Pacific Northwest National Laboratory in Richland, Washington. For example, sulfates that form from coal-plant exhaust reflect sunlight back into space, acting to shade the planet and cool it off. Black-carbon particles from diesel exhaust, on the other hand, absorb sunlight and heat up, warming the atmosphere.
“When you add them together, we think that on balance they’re cooling the planet,” Rasch says. That is, they mask some of the temperature increase that would have occurred as a result of carbon dioxide emissions, the main human contribution to global warming. But this effect would be more significant if the particulates that help heat up the atmosphere were removed. “If we could get rid of the ones that are warming the planet,” he says, “then that would buy us some more time.”